The calculator considers a scenario where a compressed gas cylinder containing a single gas is being used in a workplace or room. It estimates what would happen if the entire contents of that gas cylinder were released into the room all at once.
It does this by first determining how much gas is actually stored inside the cylinder based on the cylinder's size and the pressure it's filled to.
Next, it compares the volume of gas that could be released from the cylinder to the free air volume of the room or workplace. This allows it to calculate the percentage of the gas in the air after the gas has displaced the initial contents of the air.
If the concentration of the gas in the air is within a toxic exposure limit, or above a certain proportion of the lower explosive limit, it means there could be a risk of toxic exposure would could lead to long-term health complications. Alternatively, the ability for a self-sustaining fire to be caused can increase.
For asphyxiant gases, this displacement reduces the available oxygen for a person to breathe.
If the estimated oxygen level falls below a certain threshold, it means there could be a risk of oxygen deficiency to a person within that room, leading to light-headedness, fainting or, ultimately, hypoxia and death by asphyxiation.
The calculator shows what the worst-case scenario could be, and it suggests to the user whether a detection system may or may not be necessary.
If you have a compressed gas cylinder, and you don't know the volume of gas complete sections 1 and 3.
If you have a liquefied gas cylinder and you don't know the volume of gas, complete sections 2 and 3.
If you know the volume of gas that could expand into the room, complete section 3.
To use this calculator, you will need to know:
| Compressed Gas | Liquefied gas |
|---|---|
| Pressure of cylinder (bar) | Weight of gas in cylinder (kg) |
| *Cylinder water capacity (L) | **Specific volume (m³/kg) |
After calculating the volume of the gas released, compare your calculated percentage volume or ppm with the relevant limit for the released gas:
For asphyxiant gases:
The remaining oxygen concentration should be compared to the accepted lower limit (19.5% concentration).
For toxic gases:
You should take the % value calculated in section 3 and compare this to the Workplace Exposure Limit value in
EH40
Note: You may need to convert your percentage value to ppm (by multiplying the % by 10,000)
For flammable gases:
You should take the % value calculated in section 3 and compare this to the lower explosive limit for the gas.
A list of these can be located in the Engineering Toolbox
The percentage concentration calculated must not exceed 25% of the lower explosive limit.
For oxygen/carbon dioxide enrichment:
You should take the % value calculated in section 3 and compare this to the upper limit for the gas in use (0.5% for CO2 and 23.5% for O2)
If you do not know the free air volume of the location the calculation is being carried out in, ensure you tick the box to indicate this. This will reduce the volume by 40% to provide a conservative estimate of the free air volume.